Prediction Equations For The Net Energy Content Of Soybean Meal In Growing Pigs

Four energy metabolism experiments were conducted to determine predication equations for net energy content (NE) of soybean meal in growing pigs using open-circuit respiratory chambers. A total of138crossbred barrows (Duroc×Large White×Landrace) were used in this study. In Exp.1,18crossbred barrows with an initial body weight of35±1.3kg were used to determine the net energy content of soybean protein isolate in growing pigs by the difference or regression method. Dietary treatments were a basal diet and5experiment diets that replaced the basal diet with5%,8%,11%,14%, and17%soybean protein isolate. Each diet was fed to6barrows according to a pseudo Latin square design. Each diet was fed for15d, including a5-d adjustment period, and a9-d period for collection of feces and urine to measure the digestible (DE) and metabolizable energy (ME) of the diets. Pigs were kept individually in respiration chambers for the last4d of the fecal collection period and heat production was measured daily. An additional day was used to determine the fasting heat production (FHP). Retained energy was measured as the difference between ME intake and total heat production. Net energy was calculated as retained energy plus FHP. According to the difference method, which replaced11%-17%of the basal diet, the average DE, ME, and NE values of soy protein isolate were18.46,18.13, and12.16MJ/kg, whereas the values obtained by the regression method were18.70,18.28, and11.89MJ/kg, respectively. The NE:ME ratio was approximately66%for soy protein isolate. In Exp.2, a total of36growing (27±2.2kg) and36finishing (70±2.6kg) pigs were selected to determine their maintenance energy requirement. Pigs were assigned to one of6feeding levels. Dietary treatments were calculated as0%,20%,40%,60%,80%, and100%of their estimated ad libitum ME intake (2,500kJ ME/kg BW0.6·d-1). The measurements were conducted on6pigs per feeding level and per stage. After a5-d adjustment period, barrows in the0%treatment were kept in respiration chambers for one day to measure the fasting heat production. Barrows in the other treatments were kept individually in6respiration chambers for a5-d balance trial followed by24h fasting period. Heat production in the fed state was measured and feces were collected in the balance trial. The results show that the daily heat production increased (P<0.01) between extreme feeding levels. FHP increased when the feeding level increased (P<0.01) and was lower (P=0.01) during the second stage than during the first stage of pig growth. The efficiencies of using ME for growth and for maintenance were estimated as66%and78%for both growing and finishing pigs. Net energy for maintenance (NEm) is equal to758and732kJ/kg BW0.6·d-1for growing pigs and finishing pigs, respectively. In Exp.3,24pigs (30±2.5kg) were used to determine the net energy of of soybean meals by the difference method for growing pigs. Dietary treatments were a basal diet and5experimental diets which replaced the basal diet with25%of five different soybean meals. Each diet was fed for10d, including a5-d adjustment period, and a5-d nitrogen and energy balance measurement period. The net energy of the diets was calculated as the FHP (758kJ/kg BW0.6·d-1) plus retained energy. The results indicate that diets containing soybean meal had a lower NE (P<0.05) and a higher (P<0.05) total heat production than the basal diet. The NE value of soybean meal ranged from9.00to9.42MJ/kg DM. In Exp.4,24pigs (28±2.2kg) were used to determine the net energy of simulated soybean meal for growing pigs. Five simulated soybean meals were prepared by mixing soybean meals with different percentage of a soybean hull. The experimental design was similar to Exp.3. The results show that the NE content of simulated soybean meals ranged from8.19to9.14MJ/kg DM. The efficiency of using ME for NE ranged from54.18%-58.00%. Stepwise regression equations were calculated to predict DE, ME, and NE from crude nutrient levels in both soybean meals and simulated soybean meals. The best parameters were crude fiber (CF), ether extract (EE), sucrose (SUc), and nitrogen free extract (NEF). The best equations for predicting DE, ME, and NE (MJ/kg DM) were as follows:DE=15.35+0.58EE+0.34SUc-0.15CF, R2=0.98; ME=13.36+0.50SUc+0.75EE-0.14CF, R2=0.98; NE=12.19-0.05NEF-0.14CF, R2=0.95.